Fibers made from soluble polymers

ABSTRACT

A fiber can be made having a structure with an axial core and a coating layer. The fiber can have a polymer core and one or two layers surrounding the core. The fine fiber can be made from a polymer material and a resinous aldehyde composition such that the general structure of the fiber has a polymer core surrounded by at least a layer of the resinous aldehyde composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationSer. No. 61/537,171, filed on Sep. 21, 2011, which is incorporatedherein by reference in its entirety.

BACKGROUND OF THE DISCLOSURE

Recent technologies have been used to form layers of fine fiber. Finefiber technologies that contemplate polymeric materials mixed or blendedwith a variety of other substances are disclosed in, for example Chunget al., U.S. Pat. No. 6,743,273. These fibers have found commercialacceptance in certain filtration applications in which a layer of finefiber is formed on a filtration substrate. Certain of the disclosedfibers comprise an axial core comprising a phase comprising polymermaterials. Surrounding the axial core can be found a layer of a coatingmaterial such as a phenolic oligomer or a fluoropolymer component.

In the formation of these fibers, a solution of the polymer and additiveis formed by melt processes or electrospun to form the fiber. In certainfiber-making processes, solvents that are safe and easy to use aredesired in industrial applications. Fibers formed using such solventsoften need to survive and perform well in a wide variety ofenvironments.

SUMMARY

A unique fiber material is foamed by mixing or blending a polymermaterial with a resinous aldehyde composition. The resinous aldehydecomposition is one that can self-crosslink and the polymer is one thatis nonreactive with the resinous aldehyde composition.

In certain embodiments, when fowled into a fiber, the mixture or blendof nonreactive polymer material and resinous aldehyde composition formsa uniform (i.e., homogeneous) mixture (i.e., blend) of the twocomponents in a semi-interpenetrating network morphology.

In certain embodiments, when foamed into a fiber, the mixture or blendof nonreactive polymer material and resinous aldehyde composition, atappropriate ratios, preferably forms at least two (e.g., concentric orcoaxial) phases. The first phase is an internal core or axial polymerphase that includes the polymer material as the predominant material.Herein, “internal core,” “core phase,” “first phase,” and “axial phase”are used interchangeably. The first core phase is surrounded by a second(coating) phase that includes the resinous aldehyde composition as thepredominant material.

Thus, the present disclosure provides a fiber (preferably, a fine fiber)comprising a core phase and a coating phase, wherein the core phasecomprises a polymer and the coating phase comprises a resinous aldehydecomposition.

With the use of appropriate ratios of polymer material and resinousaldehyde composition in the fiber formation, in some embodiments, thefiber comprises three phases. In this embodiment, an internal axialpolymer phase includes the polymer material as the predominant materialor major amount, with negligible self-crosslinked resinous aldehydecomposition (if present, it is only present in a minor phase).Surrounding the internal axial polymer phase is a second phase (i.e., atransition layer or transition phase) comprising a mixture of thepolymer material and a self-crosslinked resinous aldehyde (typically,there are equivalent amounts of polymer and resinous aldehyde present inthis transition phase). The fiber additionally contains a third exteriorphase (i.e., the outermost coating) comprising resinous aldehyde as thepredominant or major component.

Thus, the present disclosure also provides a fiber (e.g., a nanofiber ormicrofiber, and preferably a fine fiber as described herein) comprisinga core phase and a coaxial coating phase; wherein the core phasecomprises a nonreactive polymer and the coating phase comprises aresinous melamine-aldehyde composition; wherein a negligible portion ofthe nonreactive polymer is crosslinked by the resinous melamine-aldehydecomposition; and further wherein the fine fiber is prepared from aresinous melamine-aldehyde composition in an amount of greater than 20parts by weight per 100 parts by weight of the nonreactive polymer.

Herein, a fiber has an average fiber diameter of typically no greaterthan 100 microns. Typically, this means that a sample of a plurality offibers of the present disclosure has an average fiber diameter of nogreater than 100 microns. A preferred “fine” fiber has an average fiberdiameter of no greater than 10 microns.

The fiber of the present disclosure is preferably prepared from aresinous aldehyde composition comprising alkoxy groups and other groupscapable of self-crosslinking (e.g., by condensation) and a nonreactivepolymer, wherein the weight ratio of resinous aldehyde composition topolymer is preferably greater than 20:100.

In these embodiments, a layer of fine fibers can be manufactured byforming a plurality of fine fibers on a filtration substrate, therebyforming a filter media. The filter media (i.e., fine fiber layer plusfiltration substrate) can then be manufactured into filter elements(i.e., filtration elements), including, e.g., flat-panel filters,cartridge filters, or other filtration components.

The terms “comprises” and variations thereof do not have a limitingmeaning where these terms appear in the description and claims.

The words “preferred” and “preferably” refer to embodiments of thedisclosure that may afford certain benefits, under certaincircumstances. However, other embodiments may also be preferred, underthe same or other circumstances. Furthermore, the recitation of one ormore preferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the disclosure.

In this application, terms such as “a,” “an,” and “the” are not intendedto refer to only a singular entity, but include the general class ofwhich a specific example may be used for illustration. The terms “a,”“an,” and “the” are used interchangeably with the term “at least one.”

The phrases “at least one of” and “comprises at least one of” followedby a list refers to any one of the items in the list and any combinationof two or more items in the list.

As used herein, the term “or” is generally employed in its usual senseincluding “and/or” unless the content clearly dictates otherwise. Theterm “and/or” means one or all of the listed elements or a combinationof any two or more of the listed elements.

Also herein, all numbers are assumed to be modified by the term “ ” andpreferably by the term “exactly.” As used herein in connection with ameasured quantity, the term “ ” refers to that variation in the measuredquantity as would be expected by the skilled artisan making themeasurement and exercising a level of care commensurate with theobjective of the measurement and the precision of the measuringequipment used.

Also herein, the recitations of numerical ranges by endpoints includeall numbers subsumed within that range as well as the endpoints (e.g., 1to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

The above summary of the present disclosure is not intended to describeeach disclosed embodiment or every implementation of the presentdisclosure. The description that follows more particularly exemplifiesillustrative embodiments. In several places throughout the application,guidance is provided through lists of examples, which examples can beused in various combinations. In each instance, the recited list servesonly as a representative group and should not be interpreted as anexclusive list.

DRAWINGS

The disclosure may be more completely understood in connection with thefollowing drawings, in which FIGS. 1 through 5 comprise test data andresults that demonstrate the structure and nature of fine fibermaterials made from a mixture or blend of polymer material and resinousaldehyde composition.

FIG. 1: Comparison of fiber morphology for Reference Examples 2 and 4,Example 5 (control), and Example 3.

FIG. 2: (a) Ethanol soak test for 1 min; (b) Water soak test at 140° F.for 5 min.

FIG. 3: SEM images of filter media after ethanol soak test for 1 min.Images denoted by a, b, c, d, e correspond to “as is” samples fornanofiber compositions. Images denoted by a′, b′, c′, d′, e′ correspondto “post ethanol soak” samples.

FIG. 4: Profile plots of atomic (C1s (C_P4VP and HM 2608), N1s and O1s)species obtained for P4VP/melamine resin by C60 ion gun sputtering.

FIG. 5: Pictorial representation of the fiber cross-section based onESCA/C60 results for P4VP:ME at weight ratios of (a) 1:0.2, 1:0.4 and1:0.6, and (b) 1:0.8 respectively.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Polymer webs have been made by electrospinning, melt spinning, extrusionmelt spinning, air laid processing or wet laid processing. Thefiltration efficiency of such filters is characteristic of thefiltration media and is related to the fraction of the particulateremoved from the mobile fluid stream. Efficiency is typically measuredby a set test protocol, an example of which is defined in the patentslisted below. Fine fiber technologies that contemplate polymericmaterials mixed or blended with a variety of other substances isdisclosed in Chung et al., U.S. Pat. No. 6,743,273; Chung et al., U.S.Pat. No. 6,924,028; Chung et al., U.S. Pat. No. 6,955,775; Chung et al.,U.S. Pat. No. 7,070,640; Chung et al., U.S. Pat. No. 7,090,715; Chung etal., U.S. Patent Publication No. 2003/0106294; Barris et al., U.S. Pat.No. 6,800,117; and Gillingham et al., U.S. Pat. No. 6,673,136.Additionally, in Ferrer et al., U.S. Pat. No. 7,641,055, awater-insoluble, high-strength polymer material is made by mixing orblending a polysulfone polymer with a polyvinyl pyrrolidone polymerresulting in a single phase polymer alloy used in electrospinning finefiber materials. While the fine fiber materials discussed above haveadequate performance for a number of filtration end uses, inapplications with extremes of temperature ranges, where mechanicalstability is required, improvements in fiber properties can always bemade.

The fibers of the present disclosure are made by combining afiber-forming polymer material and a resinous aldehyde composition thatincludes reactive groups for self-crosslinking, such as a reactivemelamine-formaldehyde resin. In this context, “reactive” means that theresin includes one or more functional groups capable ofself-crosslinking but not reacting with one or more polymers used inmaking the fine fibers. Herein, “resin” or “resinous” refers tomonomers, oligomers, and/or polymers, particularly of a nature that canmigrate to the surface of a fine fiber. Herein, the term “resinousaldehyde composition” refers to the starting material as well as thematerial in the final fibers. It will be understood that in the finalfibers, at least portions of the resinous aldehyde composition will beinvolved in self-crosslinking.

These components can be combined in solution or melt form. In certainembodiments, the fine fibers are electrospun from a solution ordispersion. Thus, the polymer materials and resinous aldehyde (e.g.,melamine-aldehyde) compositions are dispersible or soluble in at leastone common solvent or solvent blend suitable for electrospinning.

Referring to FIG. 5, as the fiber 100/102 forms, the resinous aldehydecomposition preferably forms at least one exterior concentric layer(i.e., phase), such as a second coating phase 22 (fiber 102) comprisingpredominantly the resinous aldehyde composition (e.g., melamine-aldehydecomposition), or two exterior concentric layers (i.e., phases) such as asecond coating phase 20 (fiber 100) comprising a mixture of the polymermaterial and a resinous aldehyde composition, and a third exterior phase(outermost phase) 30 (fiber 100) comprising predominantly the resinousaldehyde composition. That is, the resinous aldehyde composition canmigrate to the surface to form a two-phase fiber (fiber 102) or athree-phase fiber (fiber 100), in which the core 10 (fiber 100) or 12(fiber 102) comprises primarily the polymer material (e.g., poly(4-vinylpyridine) also referred to as P4VP).

In this context, “predominantly” means the referenced material ispresent in a particular region (e.g., coating, layer, or phase) in amajor amount (i.e., greater than 50% by weight) of the material in thatregion.

Preferably, the fine fiber of the present disclosure is prepared from aself-crosslinkable resinous aldehyde composition comprising reactivegroups (preferably, alkoxy groups) and a polymer comprising no, or a lowamount of, reactive groups (i.e., groups capable of reacting with thereactive groups of the resinous aldehyde composition), wherein theweight ratio of self-crosslinkable resinous aldehyde to nonreactivepolymer is at least (preferably, greater than) 20:100 (i.e., 20 partsresinous aldehyde composition to 100 parts nonreactive polymer). Morepreferably, the weight ratio of the self-crosslinkable resinous aldehydecomposition to nonreactive polymer is greater than 40:100. Even morepreferably, the weight ratio of the self-crosslinkable resinous aldehydecomposition to the nonreactive polymer is greater than 60:100.

Preferably, the weight ratio of the self-crosslinkable resinous aldehydecomposition to nonreactive polymer is no greater than 300:100. Morepreferably, the weight ratio of the self-crosslinkable resinous aldehydecomposition to the nonreactive polymer is no greater about 250:100. Evenmore preferably, the weight ratio of the self-crosslinkable resinousaldehyde composition to nonreactive polymer is no greater than 210:100.

In certain embodiments, using a weight ratio of resinous aldehydecomposition to polymer of greater than 40:100, results in apolymer/semi-interpenetrating network type structure wherein theinterpenetrating network is the self-crosslinked resinous aldehyde. Thisprovides improved properties, such as humidity resistance, to the finefibers and fine fiber layers of the invention, relative to commerciallyavailable fibers and fiber layers.

Suitable resinous aldehyde compositions include one or more reactivegroups that are capable of self-crosslinking in a fiber-making processas described herein. Such reactive groups include alkoxy groups as wellas hydroxyl, carboxylic acid, and/or —NH groups. Exemplary resinousaldehyde compositions are synthetic resins made by treating variousaldehydes with a reactant under condensation reaction conditions. Usefulsuch reactants include phenol, urea, aniline, benzoguanamine,glycoluril, and melamine. Useful resinous aldehyde compositions includealdehyde-based agents that can be used in self-crosslinking reactions.The resinous aldehyde compositions are typically nonvolatile. Theresinous aldehyde compositions should also be soluble in a solventchosen for the polymer material for processing, such as inelectrospinning. Resinous aldehyde compositions useful as crosslinkingagents include, a condensation product of urea and an aldehyde, acondensation product of phenol and an aldehyde, or a condensationproduct of melamine and an aldehyde. One useful class of crosslinkingresins includes resins based on nitrogen compounds such as melamine,urea, benzoguanamine, glycoluril, and other similar resins manufacturedby reacting an aldehyde with a nitrogen compound. Such self-crosslinkingresins are soluble in process solvents and possess reactivity with avariety of polymer species.

Useful resinous aldehyde compositions (e.g., melamine-aldehydecompositions) include crosslinking agents, and optionally othernonreactive room-temperature-stable resin components, that can becombined in solution or melt Rhin with a variety of polymer materials.Melamine forms resinous compositions with a variety of otherco-reactants.

Useful melamine-aldehyde compositions include melamine-aldehyde productsgenerally formed by the reaction between melamine and an aldehydecompound. Useful aldehyde compounds include C₁₋₆ alkanals includingformaldehyde, acetaldehyde, butyraldehyde, isobutyraldehyde, and thelike. Mixtures of such aldehydes can be used if desired. Themelamine-aldehyde resins, and other suitable resinous aldehydecompositions, include components having at least two alkoxy groups permolecule. Typical partially and fully reacted melamine-aldehydes havefrom 3 to 6, or from 4 to 6, alkoxy groups per molecule.

In certain embodiments, the resinous aldehyde composition comprises acondensation product of urea and an aldehyde, a condensation product ofphenol and an aldehyde, a condensation product of melamine and analdehyde, or a mixture thereof. In certain embodiments, the resinousaldehyde composition comprises a condensation product of benzoguanamineand an aldehyde, a condensation product of glycouril and an aldehyde, ora mixture thereof.

Useful resinous aldehyde compositions (e.g., melamine-aldehydecompositions) include compounds and mixtures thereof including:partially methylated melamine; methylated high imino melamine; highimino mixed ether melamine; n-butylated high imino and partiallyn-butylated melamine; partially iso-butylated melamine; partiallyn-butylated urea; partially iso-butylated urea; glycoluril;methoxymethyl methylol melamine resins; among others thatself-crosslink.

Various melamine compositions that self-crosslink are sold under thetrade names CYMEL available from Cytec Industries of West Paterson,N.J., wherein such compositions include, for example, CYMEL 3745, CYMELMM-100, CYMEL 3749, CYMEL 323, CYMEL 325, CYMEL 327, CYMEL 328, CYMEL370, CYMEL 373, CYMEL 385, CYMEL 1158, CYMEL 1172, CYMEL UM-15, CYMELU-64, CYMEL U-65, CYMEL U-21-571, CYMEL U-93-210, CYMEL U-216-10-LF,CYMEL U-227-8, CYMEL U-1050-10, CYMEL U-1052-8, CYMEL U-1054, CYMELUB-25-BE, CYMEL UB-30-B, CYMEL U-662, CYMEL U-663, CYMEL U-1051, CYMELUI-19-1, CYMEL UI-21E, CYMEL UI-27-EI, CYMEL UI-38-I, and the like; andvarious melamine compositions sold under the trade name LUWIPAL andavailable from the BASF AG of Ludwigshafen, Germany, wherein suchcompositions include, for example, LUWIPAL LR 8955, LUWIPAL LR 8968, andLUWIPAL LR 8984. Such resins are also available from INEOS MelaminesInc. sold under the trade names RESIMENE (e.g., RESIMENE HM2608),MAPRENAL, and MADURIT. The primary condition for such material is theability of it to self-condense (i.e., self-crosslink). Variouscombinations of resinous aldehyde compositions can be used if desired;however, such combinations will include at least one self-crosslinkingaldehyde component.

In many preferred embodiments, a melamine-formaldehyde resin (sometimesreferred to herein as simply a “melamine” composition or “melamine”resin) is used. Reference to melamine-formaldehyde resins means amelamine-based resin that has two or more (at least two) alkoxyfunctional groups (methoxy, ethoxy, propoxy, butoxy, etc.) per melaminemolecule. Besides the alkoxy functional groups, themelamine-formaldehyde resins include imine (—NH—), carboxylic acid(—C(O)OH), or hydroxyl (—OH) functional groups, or combinations thereof,to impart the ability to self-crosslink. Depending on the functionalgroups in the melamine formaldehyde resins, uncrosslinked resins can beboth water soluble and water insoluble, or soluble in organic solventssuch as alcohols, hydrocarbons (toluene, xylene, etc.) or others, or amixture of these solvents.

Melamine-formaldehyde resins are made from the reaction of formaldehydewith melamine. Melamine (chemical formula C₃H₆N₆) and formaldehyde(chemical formula CH₂O) have the following structures:

wherein melamine is 1,3,5-triazine-2,4,6-triamine; or2,4,6-triamino-s-triazine; or cyanuro triamide. A representativestructure for the melamine-formaldehyde resin is shown in structure I:

wherein in compound I, each X and each Y is independently H,—(CH₂)_(x)—O—R(R═H or (C1-C4)alkyl and x=1-4), or —(CH₂)_(y)—C(O)OH(y=1-4), and further wherein at least two of the X and Y groups are—(CH₂)_(n)—O—R(R═(C1-C4)alkyl and x=1-4), and at least one of the X andY groups is H, —(CH₂)_(x)—OH (x=1-4), and/or —(CH₂)_(y)—C(O)OH (y=1-4).Preferably if the compound has two or three —(CH₂)_(x)—O—R(R═C1-C4 alkyland x=1-4) groups, they are not on the same nitrogen substituent.

In the fibers of the disclosure, the self-crosslinkable resinousaldehyde composition of the disclosure is combined with a polymermaterial that comprises a polymer or polymer mixture or blend. Thepolymer or polymer mixture or blend is selected such that it can becombined with the resinous aldehyde composition in a solution ordispersion or in the melt. The combination of polymer material andresinous aldehyde composition, in certain embodiments, should besubstantially stable in the melt or in solution or dispersion form forsufficient time such that the fiber can be formed.

The polymer or polymer mixture or blend should include at least onefiber-forming polymer, and should include no, or very few, reactivegroups capable of being crosslinked by the resinous aldehydecomposition. Exemplary polymer reactive groups that should not bepresent include active hydrogen groups. Active hydrogen groups include,but are not limited to thiol (—SH), hydroxyl (—OH), carboxylate (—CO₂H),amido (—C(O)—NH— or —C(O)—NH₂), amino (—NH₂), or imino (—NH—), andanhydride (—COO)₂R groups (upon hydrolysis).

Polymer materials suitable for use in the polymeric compositions of thedisclosure include both addition polymer and condensation polymermaterials that are nonreactive polymers. In this context, “nonreactive”is defined as being unable to crosslink with the resinous aldehydecomposition used (as compared to reactive polymers (e.g., nylon) asdescribed in co-pending application entitled FINE FIBERS MADE FROMPOLYMER CROSSLINKED WITH RESINOUS ALDEHYDE COMPOSITION, Attorney DocketNo. 444.00010101, filed on even date herewith). For example, polymermaterials such as many polyolefins, polyvinyl chloride and other suchmaterials may be used, wherein such polymers have no groups that cancrosslink with the resinous aldehyde composition. Other nonreactivepolymers include polyacetals, polyesters, polyalkylene sulfides,polyarylene oxides, polysulfones, modified (e.g., polyether) polysulfonepolymers, poly(vinylpyridine) such as poly(4-vinylpyridine), and thelike. Preferred materials that fall within these generic classes includepolyethylene, polypropylene, poly(vinyl chloride),poly(methylmethacrylate), (and other acrylic resins), polystyrene, andcopolymers thereof (including ABA type block copolymers),poly(vinylidene fluoride), poly(vinylidene chloride), mixtures, blends,or alloys. Examples of useful block copolymers include ABA-typecopolymers (e.g, styrene-EP-styrene) (wherein “EP” refers toethylene-propylene) or AB (e.g., styrene-EP) polymers, KRATONstyrene-b-butadiene and styrene-b-hydrogenated butadiene(ethylenepropylene), available from Kraton Polymers U.S. LLC of Houston, Tex.;and SYMPATEX polyester-b-ethylene oxide, available from SympaTexTechnologies Inc. of Hampton, N.H. Various combinations of nonreactivepolymers can be used if desired.

Addition nonreactive polymers like poly(vinylidene fluoride),syndiotactic polystyrene, copolymers of vinylidene fluoride andhexafluoropropylene, polyvinyl acetate, amorphous addition polymers suchas polystyrene, poly(vinyl chloride) and its various copolymers, andpoly(methyl methacrylate) and its various copolymers can be solutionspun with relative ease because they are soluble or dispersible in avariety of solvents and solvent blends at low pressures andtemperatures. However, highly crystalline polymers like polyethylene andpolypropylene typically require high temperature, high pressure solventsor solvent blends if they are to be solution spun. Therefore, solutionspinning of the polyethylene and polypropylene is very difficult.

If desired, and depending on the resinous aldehyde composition, forexample, the self-crosslinking reaction described herein may need astrong acid catalyst such as a sulfonic acid, such as para-toluenesulfonic acid. In certain embodiments, a catalyst such as an acidcatalyst is preferably used in an amount of at least 4 wt-%, based onpolymer solids, to enhance self-crosslinking speed. Typically, no morethan 10 wt-% catalyst, such as an acid catalyst, is used in theself-crosslinking reaction of the present disclosure.

If desired, fine fibers formed from the self-crosslinking reaction of aresinous aldehyde in the presence of a nonreactive polymer material, asdescribed herein, can be enhanced, e.g., with respect to speed andextent of self-crosslinking, by exposing the fine fibers to thermaltreatment. Such thermal treatment typically includes a temperature of atleast 80° C., at least 100° C., or at least 120° C., and typically nogreater than 150° C., for typically at least 5 seconds, and typically nogreater than 10 minutes.

One aspect of the disclosure is the utility of such fiber (preferably,fine fiber) materials as they are formed into a filter structure such asfilter media. In such a structure, the fine fiber materials of thedisclosure are formed on and adhered to a filter substrate (i.e.,filtration substrate). Natural fiber and synthetic fiber substrates canbe used as the filter substrate. Examples include spunbonded ormelt-blown supports or fabrics, wovens and nonwovens of syntheticfibers, cellulosic materials, and glass fibers. Plastic screen-likematerials both extruded and hole punched, are other examples of filtersubstrates, as are ultra-filtration (UF) and micro-filtration (MF)membranes of organic polymers. Examples of synthetic nonwovens includepolyester nonwovens, polyolefin (e.g., polypropylene) nonwovens, orblended nonwovens thereof. Sheet-like substrates (e.g., cellulosic orsynthetic nonwoven webs) are the typical form of the filter substrates.The shape and structure of the filter material, however, is typicallyselected by the design engineer and depends on the particular filtrationapplication.

A filter media construction according to the present disclosure caninclude a layer of permeable coarse fibrous material (i.e., media orsubstrate) having a first surface. A first layer of fiber media(preferably, fine fiber media) is preferably disposed on the firstsurface of the layer of permeable coarse fibrous media.

Preferably, the layer of permeable coarse fibrous material comprisesfibers having an average diameter of at least 5 microns, and morepreferably at least 12 microns, and even more preferably at least 14microns. Preferably, the coarse fibers have an average diameter of nogreater than 50 microns. Thus, in an embodiment of the disclosure, thecoarse fibrous material can also include fibers of the disclosure.

Also, preferably, the permeable coarse fibrous material comprises amedia having a basis weight of no greater than 260 grams/meter² (g/m²),and more preferably no greater than 150 g/m². Preferably, the permeablecoarse fibrous material comprises a media having a basis weight of atleast 0.5 g/m², and more preferably at least 8 g/m². Preferably, thefirst layer of permeable coarse fibrous media is at least 0.0005 inch(12 microns) thick, and more preferably at least 0.001 inch thick.Preferably, the first layer of permeable coarse fibrous media is nogreater than 0.030 inch thick. Typically and preferably, the first layerof permeable coarse fibrous media is 0.001 inch to 0.030 inch (25-800microns) thick. Preferably, the first layer of permeable coarse fibrousmedia has a Frazier permeability (differential pressure set at 0.5 inchof water) of at least 2 meters/minute (m/min). Preferably, the firstlayer of permeable coarse fibrous media has a Frazier permeability(differential pressure set at 0.5 inch of water) of no greater than 900m/min.

In preferred arrangements, the first layer of permeable coarse fibrousmaterial comprises a material which, if evaluated separately from aremainder of the construction by the Frazier permeability test, wouldexhibit a permeability of at least 1 m/min, and preferably at least 2m/min. In preferred arrangements, the first layer of permeable coarsefibrous material comprises a material which, if evaluated separatelyfrom a remainder of the construction by the Frazier permeability test,would exhibit a permeability of no greater than 900 m/min, and typicallyand preferably 2-900 m/min. Herein, when reference is made toefficiency, unless otherwise specified, reference is meant to efficiencywhen measured according to ASTM-1215-89, with 0.78 micron (μ)monodisperse polystyrene spherical particles, at 20 fpm (feet perminute, 6.1 m/min) as described herein.

Fibers (preferably, fine fibers) of the disclosure can be made using avariety of techniques including electrostatic spinning, wet spinning,dry spinning, melt spinning, extrusion spinning, direct spinning, gellspinning, etc. Although the following description refers specifically to“fine” fibers (i.e., having an average fiber diameter of no greater than10 microns), it also applies to fibers of a larger fiber diameter.

Herein, a “fine” fiber has an average fiber diameter of no greater than10 microns. Typically, this means that a sample of a plurality of fibersof the present disclosure has an average fiber diameter of no greaterthan 10 microns. Preferably, such fibers have an average diameter of nogreater than 5 microns, more preferably no greater than 2 microns, evenmore preferably no greater than 1 micron, and even more preferably nogreater than 0.5 micron. Preferably, such fibers have an averagediameter of at least 0.005 micron, more preferably at least 0.01 micron,and even more preferably at least 0.05 micron.

The fine fibers are collected on a support layer during, for example,electrostatic or melt spinning formation, and are often heat treatedafter fiber making. Preferably, the layer of fine fiber material isdisposed on a first surface of a layer of permeable coarse fibrous media(i.e., support layer) as a layer of fiber. Also, preferably the firstlayer of fine fiber material disposed on the first surface of the firstlayer of permeable coarse fibrous material has an overall thickness thatis no greater than 50 microns, more preferably no greater than 30microns, even more preferably no more than 20 microns, and mostpreferably no greater than 10 microns. Typically and preferably, thethickness of the fine fiber layer is within a thickness of 1-20 times(often 1-8 times, and more preferably no more than 5 times) the finefiber average diameter used to make the layer. In certain embodiments,the fine fiber layer has a thickness of at least 0.05μ.

In a fiber spinning process for making fine fibers of the disclosure,the polymer being spun is typically converted into a fluid state (e.g.,by dissolution in solvent or melting). The fluid polymer is then forcedthrough the spinneret, where the polymer cools to a rubbery state, andthen a solidified state. The aldehyde composition can migrate to thesurface as the fluid polymer transitions to a solid state. Wet spinningis typically used for polymers that need to be dissolved in a solvent tobe spun. The spinneret is submerged in a chemical bath that causes thefiber to precipitate, and then solidify, as it emerges. The process getsits name from this “wet” bath. Acrylic, rayon, aramid, modacrylic, andspandex are produced via this process. Dry spinning is also used forpolymers that are dissolved in solvent. It differs in that thesolidification is achieved through evaporation of the solvent. This isusually achieved by a stream of air or inert gas. Because there is noprecipitating liquid involved, the fiber does not need to be dried, andthe solvent is more easily recovered. Melt spinning is used for polymersthat can be melted. The polymer solidifies by cooling after beingextruded from the spinneret.

In a typical process, pellets or granules of the solid polymer are fedinto an extruder.

The pellets are compressed, heated and melted by an extrusion screw,then fed to a spinning pump and into the spinneret. A direct spinningprocess avoids the stage of solid polymer pellets. The polymer melt isproduced from the raw materials, and then from the polymer finisherdirectly pumped to the spinning mill Direct spinning is mainly appliedduring production of polyester fibers and filaments and is dedicated tohigh production capacity (>100 tons/day). Gel spinning, also known asdry-wet spinning, is used to obtain high strength or other specialproperties in the fibers. The polymer is in a “gel” state, onlypartially liquid, which keeps the polymer chains somewhat boundtogether. These bonds produce strong inter-chain forces in the fiber,which increase its tensile strength. The polymer chains within thefibers also have a large degree of orientation, which increasesstrength. The fibers are first air dried, then cooled further in aliquid bath. Some high strength polyethylene and aramid fibers areproduced via this process.

An alternative for making fine fibers of the disclosure is amelt-blowing process. Melt-blowing (MB) is a process for producingfibrous webs or articles directly from polymers or resins usinghigh-velocity air or another appropriate force to attenuate thefilaments. This process is unique because it is used almost exclusivelyto produce microfibers rather than fibers the size of normal textilefibers. MB microfibers generally have diameters in the range of 2 to 4μm (micrometers or microns or μ), although they may be as small as 0.1μm and as large as 10 to 15 μm. Differences between MB nonwoven fabricsand other nonwoven fabrics, such as degree of softness, cover oropacity, and porosity can generally be traced to differences in filamentsize. As soon as the molten polymer is extruded from the die holes, highvelocity hot air streams (exiting from the top and bottom sides of thedie nosepiece) attenuate the polymer streams to form microfibers. As thehot air stream containing the microfibers progresses toward thecollector screen, it entrains a large amount of surrounding air (alsocalled secondary air) that cools and solidifies the fibers. Thesolidified fibers subsequently get laid randomly onto the collectingscreen, forming a self-bonded nonwoven web. The fibers are generallylaid randomly (and also highly entangled) because of the turbulence inthe air stream, but there is a small bias in the machine direction dueto some directionality imparted by the moving collector. The collectorspeed and the collector distance from the die nosepiece can be varied toproduce a variety of melt-blown webs. Usually, a vacuum is applied tothe inside of the collector screen to withdraw the hot air and enhancethe fiber laying process.

Any of the above-listed processes for making the fine fiber of thedisclosure can be used to make the permeable course fibrous material forthe filtration substrate. Spunbond techniques can also be used formaking the permeable course fibrous material for the filtrationsubstrate. Spunbond fabrics are produced by depositing extruded, spunfilaments onto a collecting belt in a uniform random manner followed bybonding the fibers. The fibers are separated during the web layingprocess by air jets or electrostatic charges. The collecting surface isusually perforated to prevent the air stream from deflecting andcarrying the fibers in an uncontrolled manner. Bonding imparts strengthand integrity to the web by applying heated rolls or hot needles topartially melt the polymer and fuse the fibers together. Since molecularorientation increases the melting point, fibers that are not highlydrawn can be used as thermal binding fibers. Polyethylene or randomethylene-propylene copolymers are used as low melting bonding sites.Spunbond products are employed in carpet backing, geotextiles, anddisposable medical/hygiene products. Since the fabric production iscombined with fiber production, the process is generally more economicalthan when using staple fiber to make nonwoven fabrics. The spinningprocess is similar to the production of continuous filament yarns andutilizes similar extruder conditions for a given polymer. Fibers areformed as the molten polymer exits the spinnerets and is quenched bycool air. The objective of the process is to produce a wide web and,therefore, many spinnerets are placed side by side to generatesufficient fibers across the total width. The grouping of spinnerets isoften called a block or bank. In commercial production two or moreblocks are used in tandem in order to increase the coverage of fibers.

In a spunbond process, before deposition on a moving belt or screen, theoutput of a spinneret usually consists of a hundred or more individualfilaments which must be attenuated to orient molecular chains within thefibers to increase fiber strength and decrease extensibility. This isaccomplished by rapidly stretching the plastic fibers immediately afterexiting the spinneret. In practice the fibers are accelerated eithermechanically or pneumatically. In most processes the fibers arepneumatically accelerated in multiple filament bundles; however, otherarrangements have been described where a linearly aligned row or rows ofindividual filaments is pneumatically accelerated.

In a traditional textile spunbond process some orientation of fibers isachieved by winding the filaments at a rate of approximately 3,200 m/minto produce partially oriented yarns (POY). The POYs can be mechanicallydrawn in a separate step for enhancing strength. In spunbond productionfilament bundles are partially oriented by pneumatic acceleration speedsof 6,000 m/min or higher. Such high speeds result in partial orientationand high rates of web formation, particularly for lightweight structures(17 g/m²). The formation of wide webs at high speeds is a highlyproductive operation.

For many applications, partial orientation of the course fibers of thefilter substrate sufficiently increases strength and decreasesextensibility to give a functional fabric (examples: diaper coverstock). However, some applications, such as primary carpet backing,require filaments with very high tensile strength and low degree ofextension. For such application, the filaments are drawn over heatedrolls with a typical draw ratio of 3.5:1. The filaments are thenpneumatically accelerated onto a moving belt or screen. This process isslower, but gives stronger webs.

The spunbond web is formed by the pneumatic deposition of the filamentbundles onto the moving belt. A pneumatic gun uses high-pressure air tomove the filaments through a constricted area of lower pressure, buthigher velocity as in a venturi tube. In order for the web to achievemaximum uniformity and cover, individual filaments can be separatedbefore reaching the belt. This is accomplished by inducing anelectrostatic charge onto the bundle while under tension and beforedeposition. The charge may be induced triboelectrically or by applying ahigh voltage charge. The former is a result of rubbing the filamentsagainst a grounded, conductive surface. The electrostatic charge on thefilaments can be at least 30,000 000 electrostatic units per squaremeter (esu/m²).

Fibers (preferably, fine fibers) of the disclosure can be madepreferably using the electrostatic spinning process. A suitableelectrospinning apparatus for forming the fine fibers includes areservoir in which the fine fiber forming solution is contained, and anemitting device, which generally consists of a rotating portionincluding a plurality of offset holes. As it rotates in theelectrostatic field, a droplet of the solution on the emitting device isaccelerated by the electrostatic field toward the collecting media.Facing the emitter, but spaced apart therefrom, is a grid upon which thecollecting media (i.e., a substrate or combined substrate) ispositioned. Air can be drawn through the grid. A high voltageelectrostatic potential is maintained between emitter and grid by meansof a suitable electrostatic voltage source. The substrate is positionedin between the emitter and grid to collect the fiber.

Specifically, the electrostatic potential between grid and the emitterimparts a charge to the material which cause liquid to be emittedtherefrom as thin fibers which are drawn toward grid where they arriveand are collected on substrate. In the case of the polymer in solution,a portion of the solvent is evaporated off the fibers during theirflight to the substrate. The fine fibers bond to the substrate fibers asthe solvent continues to evaporate and the fiber cools. Electrostaticfield strength is selected to ensure that as the polymer material isaccelerated from the emitter to the collecting media, the accelerationis sufficient to render the polymer material into a very thin microfiberor nanofiber structure. Increasing or slowing the advance rate of thecollecting media can deposit more or less emitted fibers on the formingmedia, thereby allowing control of the thickness of each layer depositedthereon. Electrospinning processes usually use polymer solutions with5-20% solids (on polymer) concentration. Solvents that are safe and easyto use are desired in industrial applications. On the other hand, fibersformed with such solvents often need to survive and perform in a widevariety of environments.

Filter media with high removal efficiency can be manufactured utilizingthe polymers and fibers from this disclosure. Typical properties of thefilter media are shown in Table 1. In Table 1, LEFS efficiency (LowEfficiency Flat Sheet) refers to the removal efficiency for 0.78 micronlatex particles at a face velocity of 20 feet/minute (ft/min) whentested according to ASTM-1215-89.

TABLE 1 Typical Fiber Parameters Fiber (size) diameter 0.01-2 0.05-0.80.1-0.5 (μ) Layer thickness  0.1-8 0.4-5  0.8-4   (μ) Efficiency Atleast 75%   75-90%   80-85% (LEFS)

The fibers (preferably, fine fibers) of the present disclosure in thefaun of a layer disposed on a filtration substrate can then bemanufactured into filter elements, including flat-panel filters,cartridge filters, or other filtration components. Examples of suchfilter elements are described in U.S. Pat. Nos. 6,746,517; 6,673,136;6,800,117; 6,875,256; 6,716,274; and 7,316,723.

EXEMPLARY EMBODIMENTS

1. A fiber comprising a nonreactive polymer and a self-crosslinkedresinous aldehyde composition.

2. The fiber of embodiment 1 wherein the nonreactive polymer andself-crosslinked resinous aldehyde composition forms a uniform mixturein a semi-interpenetrating network morphology.

3. The fiber of embodiment 1 wherein the fiber comprises a core phaseand a coating phase; wherein the core phase comprises a nonreactivepolymer and the coating phase comprises a self-crosslinked resinousaldehyde composition.

4. The fiber of embodiment 3 comprising two phases, wherein the corephase comprises a mixture of the polymer and the resinous aldehydecomposition.

5. The fiber of embodiment 3 comprising three phases, wherein the corephase comprises the polymer, the coating phase comprises the resinousaldehyde composition, and a transition phase comprises a mixture of thepolymer and the resinous aldehyde composition.

6. The fiber of any one of embodiments 1 through 4 which is preparedfrom a resinous aldehyde composition comprising reactive alkoxy groupsand a nonreactive polymer.

7. The fiber of any one of embodiments 1 through 6 wherein the resinousaldehyde composition is present in an amount of greater than 20 parts byweight per 100 parts by weight of the polymer.

8. The fiber of any one of embodiments 1 through 7 which is a finefiber.

9. The fiber of any one of embodiments 1 through 8 wherein the resinousaldehyde composition comprises a resinous formaldehyde composition.

10. The fiber of embodiment 9 wherein the resinous formaldehydecomposition comprises a resinous melamine-formaldehyde composition.

11. The fiber of any one of embodiments 1 through 8 wherein the resinousaldehyde composition comprises a melamine-aldehyde composition; andwherein the aldehyde comprises formaldehyde, acetaldehyde,butyraldehyde, isobutyraldehyde, or mixtures thereof.

12. The fiber of any one of embodiments 1 through 8 wherein the resinousaldehyde composition comprises a condensation product of urea and analdehyde, a condensation product of phenol and an aldehyde, acondensation product of melamine and an aldehyde, or a mixture thereof.

13. The fiber of any one of embodiments 1 through 8 wherein the resinousaldehyde composition comprises a condensation product of benzoguanamineand an aldehyde, a condensation product of glycoluril and an aldehyde,or a mixture thereof.

14. A fine fiber comprising a core phase and a coating phase; whereinthe core phase comprises nonreactive polymer and the coating phasecomprises a self-crosslinked resinous melamine-aldehyde composition;wherein the fine fiber is prepared from a resinous melamine-aldehydecomposition in an amount of greater than 20 parts by weight per 100parts by weight of the nonreactive polymer.

15. A filter media comprising a filtration substrate and a layercomprising a plurality of fine fibers of any one of embodiments 1through 14 disposed on the substrate.

16. The filter media of embodiment 15 wherein the fine fiber layer has athickness of 0.05μ to 30μ.

17. The filter media of embodiment 15 or embodiment 16 wherein thefiltration substrate is a non-woven substrate.

18. The filter media of any one of embodiments 15 through 17 wherein thefine fiber layer is an electrospun layer and the filtration substratecomprises a cellulosic or synthetic nonwoven.

19. The fine fiber media of any one of embodiments 15 through 17 whereinthe filtration substrate comprises a polyester nonwoven, a polyolefinnonwoven, or a blended nonwoven thereof.

20. The fine fiber media of embodiment 19 wherein the filtrationsubstrate comprises polypropylene nonwoven.

21. The fine fiber media of embodiment 15 wherein the filtrationsubstrate comprises a spunbonded or melt-blown support.

22. A filter element comprising a fine fiber media of any one ofembodiments 15 through 21.

EXAMPLES

Objects and advantages of this disclosure are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this disclosure.

Test Procedures ESCA

Electron spectroscopy or chemical analysis (ESCA, also known as x-rayphotoelectron spectroscopy or XPS) is a surface analysis technique usedfor obtaining chemical information about the surfaces of solidmaterials. The materials characterization method utilizes an x-ray beamto excite a solid sample resulting in the emission of photoelectrons. Anenergy analysis of these photoelectrons provides both elemental andchemical bonding information about a sample surface. The relatively lowkinetic energy of the photoelectrons gives ESCA a sampling depth ofapproximately 3 Å. ESCA can detect all elements from lithium to uraniumwith detection limits of approximately 0.1 atomic percent. The principaladvantage of ESCA is its ability to look at a broad range of materials(polymers, glasses, fibers, metals, semi-conductors, paper, etc.) and toidentify surface constituents as well as their chemical state. This testcan be used as an indicator of migration of the aldehyde compound to thesurface of the fiber.

Ethanol Soak Test

A sample of fine fibers in the form of a layer disposed on a substrateis submerged in ethanol (190 proof) under ambient conditions. After 1minute, the sample is removed, dried, and evaluated for the amount offine fiber layer efficiency retained as determined according to theprocedure described in U.S. Pat. No. 6,743,273 (“Fine fiber layerefficiency retained”). The amount of fine fiber retained is reported asa percentage of the initial amount of fine fibers and referred to as“fine fiber layer efficiency retained.” This gives a good indication ofwhether the degree of crosslinking achieved was sufficient to protectthe bulk material from attack/dissolution to ethanol.

Hot Water Soak Test

A sample of fine fibers in the form of a layer disposed on a substrateis submerged in water previously heated to a temperature of 140° F.After 5 minutes, the sample is removed, dried, and evaluated for theamount of fine fiber layer efficiency retained as determined accordingto the procedure described in U.S. Pat. No. 6,743,273 (“Fine fiber layerefficiency retained”). The amount of fine fiber retained is reported asa percentage of the initial amount of fine fibers and referred to as“fine fiber layer efficiency retained.” This gives a good indication ofwhether the degree of crosslinking achieved was sufficient to protectthe bulk material from attack/dissolution to hot water.

Preparation of Fine Fibers Reference Examples

Reference Example 1 (Example 5 of Chung et al., U.S. Pat. No. 6,743,273)utilizes the formation of a surface coating layer by incorporatingoligomers of p-tert-butyl phenol, an additive that protects fine fibersfrom wet environments.

An alternate method to improve environmental resistance involvesblending a self-crosslinkable polymer and a non-self-crosslinkablepolymer, resulting in the formation of a structure that is analogous toan IPN (interpenetrating network) or semi-IPN (semi-interpenetratingnetwork) wherein the non-crosslinkable polymer does not redissolve afterelectrospinning and heat treatment. Reference Example 2 (Example 6 ofChung et al., U.S. Pat. No. 6,743,273) describes how such a structurecan be achieved.

Finally, Reference Example 3 (Example 6B of Chung et al., U.S. Pat. No.6,743,273) combines three important components: a non-selfcrosslinkablefiber-forming polymer, a self-crosslinkable fiber-forming polymer, and anoncrosslinkable surface-forming additive.

Reference Example 4

Nylon copolymer resin (SVP 651 obtained from Shakespeare Co., Columbia,S.C., a terpolymer having a number average molecular weight of21,500-24,800 comprising 45% nylon-6, 20% nylon-6,6 and 25% nylon-6,10)solutions were prepared by dissolving the polymer in alcohol (ethanol,190 proof) and heating to 60° C. to produce a 9% solids solution. Aftercooling, to the solution was added a melamine-formaldehyde resin (i.e.,crosslinking agent) (CYMEL 1133 obtained from Cytec Industries of WestPaterson, N.J.). The weight ratio of melamine-formaldehyde resin tonylon was 40:100 parts by weight. Additionally, to the solution wasadded para-toluene sulfonic acid (7%, based on polymer solids). Thesolution was agitated until uniform and was then electrospun to form alayer of fine fiber on a filtration substrate. For this example avoltage of 50 kV was used to form the fine fiber layer on a substratematerial moving at a line speed of 5 ft/min at a distance 4 inches fromthe emitter. The substrate material was a wetlaid cellulose media fromHollingsworth and Vose (Grade FA 448) with an average basis weight of68.6 lbs/3000 ft², average thickness of 0.011 inch (in), and averageFrazier permeability of 16 ft/min. The fine fibers disposed on thesubstrate were thermally treated at 140° C. for 10 minutes.

Example 1

The materials tested for filtration efficiency as shown in FIG. 2 weremanufactured as follows. Poly(4-vinyl pyridine) resin (“P4VP”) solutionswere prepared by dissolving the polymer (8%) in 190 proof ethanol/watermixture (90:10 weight ratio). The homopolymer (P4VP) employed has aviscosity average molecular weight of about 200,000 (ScientificPolymer). To the solution was added melamine-formaldehyde crosslinkingagent (RESIMENE HM2608 obtained from INEOS Melamines Inc., “ME”), anamount of about 20:100 parts by weight of resin:polymer content.Additionally to the solution was added para-toluene sulfonic acid (7wt-%, based on polymer solids). The solution was agitated until uniformand was then electrospun to form a layer of fine fiber on a filtrationsubstrate. For this example a voltage of 50 kV was used to form the finefiber layer on a substrate material moving at a line speed of 5 ft/minat a distance 4 inches from the emitter. The substrate material was awetlaid cellulose media from Hollingsworth and Vose (Grade FA 448) withan average basis weight of 68.6 lbs/3000 ft², average thickness of 0.011inch (in), and average Frazier permeability of 16 ft/min. The finefibers disposed on the substrate were thermally treated at 140° C. for10 minutes. The composite media layer Ruined had an initial LEFSefficiency of 90% and an initial pressure drop of 0.81 in of water. Inthis context, “initial” means prior to any ethanol or water soaktesting.

Examples 2-5

Example 1 was repeated except using the melamine-formaldehyde agent andP4VP in weight ratios of ME:P4VP of 40:100 (Example 2), 60:100 (Example3), 80:100 (Example 4) and 0:100 (Example 5). For Examples 2-4,poly(4-vinyl pyridine) resin (P4VP) solutions were prepared bydissolving the polymer (8%) in 190 proof ethanol/water mixture (90:10 wtratio). For Example 5, poly(4-vinyl pyridine) resin a 10% (P4VP)solution was prepared. Example 2 had an initial LEFS efficiency of 92%and an initial pressure drop of 0.82 inch of water. Example 3 had aninitial LEFS efficiency of 90.6% and an initial pressure drop of 0.84inch of water. Example 4 had an initial LEFS efficiency of 86.4% and aninitial pressure drop of 0.85 in of water. Finally, for Example 5, whichis the control (no self-crosslinking resin added), an intial LEFSefficiency of 77% was obtained with a pressure drop of 0.83 in of water.In this context, “initial” means prior to any ethanol or water soaktesting. The results are tabulated in Table 2 below.

TABLE 2 LEFS Efficiency Pressure Drop Fine Fiber Polymer (composite)(inch H₂O) Ex 1   90 (initial) 0.81 (initial) Ex 2   92 (initial) 0.82(initial) Ex 3 90.6 (initial) 0.84 (initial) Ex 4 86.4 (initial) 0.85(initial) Ex 5   78 (initial) 0.83 (initial) Ref Ex 2 78.1 (initial)0.84 (initial) Ref Ex 4 87.8 (initial) 0.81 (initial)

Results: Bulk Properties Fiber Morphology

The fine fiber samples produced in Examples 1-5 had an average fiberdiameter of no greater than 1.0 microns. Typically, they possessedaverage fiber diameters ranging from 200 nm to 400 nm, as measured bySEM. Certain of the samples were evaluated for fiber morphology,particle capture efficiency (LEFS—particle capture efficiency at 0.8 μMlatex particles, bench operating at 20 ft/min per ASTM StandardF1215-89), humidity resistance, and crosslinking efficiency.

FIG. 1 compares the SEM images of the fibers obtained from ReferenceExample 2, Reference Example 4, and a fiber of Example 3; both fiberlayers were formed on the same substrate material. Clearly both fiberformation and the resulting fiber diameters are very similar.

Effect of Catalyst Level

The recommended catalyst level of melamine-formaldehyde resin is usuallyless than 2% of solids (for typical three-dimensional products such asfilms). In the case of one-dimensional fibers, a higher level ofcatalyst is desired to obtain sufficiently fast crosslinking speed. Itis believed that the active catalyst species has to travel along thefiber axis, instead of along usual three dimensional directions. Thus,preferred catalyst concentrations are at least 4 wt-%, based on polymersolids for preferred crosslinking rates.

Environmental Resistance

From an environmental-resistance perspective, the effects of ethanol andwater soak were tested on cellulose filter media (flat sheet) of theReference Example 2 fiber, Reference Example 4 fiber versus the finefibers of Example 3.

FIG. 2 shows that following ethanol and hot water soak the fine fiberlayer efficiency retention for the pure homopolymer fibers is zero(designated as Example 5 in FIG. 2). As the amount of theself-crosslinking melamine-formaldehyde resin (RESIMENE HM2608) isincreased, fine fiber resistance to both ethanol and water increasesdramatically. SEM images shown in FIG. 3 confirm this conclusion.

Surface Properties Surface Analysis by ESCA

In order to better understand the fine fiber morphology ESCA analysis onfine fibers made as in Examples 1-5 but collected on a stationarysubstrate for 5 minutes (referred to in FIG. 3 as Examples 1′-5′,evaluated at Evans Analytical Group, Chaska, Minn.). The C1s profile isseparated into two components: 1) contribution from theself-crosslinking melamine-formaldehyde resin (RESIMENE HM2608, “MA”)and 2) from P4VP. Separating the C1s profile ones sees an increase inthe contribution from the P4VP component with sputtering time until itbecomes constant. Correspondingly, one observes a decrease in the C iscontribution from the coating component. By looking at the contributionsfrom C—C, C—N—C, C—O etc., the approximate surface carbon chemistrieswas determined and is tabulated below. Column 3 (“C_MA”) and 4(“C_P4VP”) defines the contributions from the aldehyde resin and thenonreactive polymer, respectively.

TABLE 3 Approximate Surface^(#) Carbon Chemistries (in % of Total C)Sample Description C_MA C_P4VP Ex 1′ P4VP:MA = 1:0.2 12 88 Ex 2′ P4VP:MA= 1:0.4 24 76 Ex 3′ P4VP:MA = 1:0.6 35 65 Ex 4′ P4VP:MA = 1:0.8 67 33^(#)Obtained from the first (surface) cycle of depth profiles.

The results are indicative of a fine fiber that has a core sheath butblend type morphology. In FIG. 4 as the sputtering time increases finefiber layers are increasingly being lost. Based on the C1-s curves andtable above, it is clear that for samples of Examples 1′ to 3′, thereare 2 layers; an internal polymer layer with little or nomelamine-formaldehyde and a sheath layer with both polymer andmelamine-formaldehyde. However the majority component in the sheathlayer is still the polymer (see Table 3 above). For sample of Example4′, there are three layers; a melamine rich (major component) outersheath, a polymer rich transition (blended) phase and an axial polymerlayer with little or no melamine-formaldehyde. This conclusion issupported by following %-atomic O. The O1s contribution plotted in FIG.4 comes entirely from the self-crosslinking resin (P4VP has no oxygen).

Based on the results shown in FIG. 4, the morphology for P4VP/HM2608fine fiber can be described pictorially with two possibilities as shownin FIG. 5( a) (for Examples 1′ to 3′) and FIG. 5( b) (for Example 4′).

The complete disclosures of the patents, patent documents, andpublications cited herein are incorporated by reference in theirentirety as if each were individually incorporated. While the disclosureis susceptible to various modifications and alternative forms, specificsthereof have been shown by way of example and drawings, and will bedescribed in detail. It should be understood, however, that thedisclosure is not limited to the particular embodiments described. Onthe contrary, the intention is to cover modifications, equivalents, andalternatives falling within the spirit and scope of the disclosure.

1. A fine fiber comprising a nonreactive polymer and a self-crosslinkedresinous aldehyde composition within the fiber.
 2. The fine fiber ofclaim 1 wherein the nonreactive polymer and self-crosslinked resinousaldehyde composition forms a uniform mixture in a semi-interpenetratingnetwork morphology.
 3. (canceled)
 4. (canceled)
 5. The fine fiber ofclaim 3 comprising three phases, wherein the core phase comprises thepolymer, the coating phase comprises the resinous aldehyde composition,and a transition phase comprises a mixture of the polymer and theresinous aldehyde composition.
 6. The fine fiber of claim 3 which isprepared from a resinous aldehyde composition comprising reactive alkoxygroups and a nonreactive polymer.
 7. The fine fiber of claim 3 whereinthe resinous aldehyde composition is present in an amount of greaterthan 20 parts by weight per 100 parts by weight of the polymer.
 8. Thefine fiber of claim 1 which is a fine fiber having an average diameterof no greater than 5 microns.
 9. The fine fiber of claim 1 wherein theresinous aldehyde composition comprises a resinous formaldehydecomposition.
 10. The fine fiber of claim 9 wherein the resinousformaldehyde composition comprises a resinous melamine-formaldehydecomposition.
 11. The fine fiber of claim 1 wherein the resinous aldehydecomposition comprises a melamine-aldehyde composition; and wherein thealdehyde comprises formaldehyde, acetaldehyde, butyraldehyde,isobutyraldehyde, or mixtures thereof.
 12. The fine fiber of claim 1wherein the resinous aldehyde composition comprises a condensationproduct of urea and an aldehyde, a condensation product of phenol and analdehyde, a condensation product of melamine and an aldehyde, or amixture thereof.
 13. The fine fiber of claim 1 wherein the resinousaldehyde composition comprises a condensation product of benzoguanamineand an aldehyde, a condensation product of glycoluril and an aldehyde,or a mixture thereof.
 14. A fine fiber comprising a core phase and acoating phase; wherein the core phase comprises nonreactive polymer andthe coating phase comprises a self-crosslinked resinousmelamine-aldehyde composition; wherein the fine fiber is prepared from aresinous melamine-aldehyde composition in an amount of greater than 20parts by weight per 100 parts by weight of the nonreactive polymer. 15.A filter media comprising a filtration substrate and a layer comprisinga plurality of fine fibers of claim 1 disposed on the substrate.
 16. Thefilter media of claim 15 wherein the fine fiber layer has a thickness of0.05μ, to 30μ.
 17. The filter media of claim 15 wherein the filtrationsubstrate is a non-woven substrate.
 18. The filter media of claim 15wherein the fine fiber layer is an electrospun layer and the filtrationsubstrate comprises a cellulosic or synthetic nonwoven.
 19. The filtermedia of claim 15 wherein the filtration substrate comprises a polyesternonwoven, a polyolefin nonwoven, or a blended nonwoven thereof.
 20. Thefilter media of claim 15 wherein the filtration substrate comprisespolypropylene nonwoven.
 21. The filter media of claim 15 wherein thefiltration substrate comprises a spunbonded or melt-blown support.
 22. Afilter element comprising a filter media of claim 15.